The first observation of above-threshold ionization was made using xenon gas.
Notes on verification
Confirmed by original 1979 Physical Review Letters paper by Agostini et al., corroborated by Agostini's own Nobel Prize biographical account and multiple secondary physics literature sources. [tier=gold indep_score=0.867 clusters=3 claim_tier=notable]
Sources
- Above-threshold ionization (wikipedia)
- https://www.nobelprize.org/prizes/physics/2023/agostini/biographical/ (corroboration)
- http://link.aps.org/doi/10.1103/PhysRevLett.42.1127 (corroboration)
- https://www.researchgate.net/publication/47418183_Above-Threshold_Ionization_As_a_Probe_of_Multielectron_Physics (corroboration)